The invention relates to the field of delivery of video-on-demand (VOD). More particularly, the invention relates to identification of an audio/video signal path from a video server to a subscriber terminal.
Typically, cable TV networks, such as CNN and video programming from a VOD server, transmit audio/video programming signals from a cable hub or a headend facility to one or more cable subscribers via a hybrid fiber optic and coaxial cable (HFC) television network. In accordance with National Television Standards Committee (NTSC), the video signals are carried in 6 MHz channel slots that are kept separate by using frequency division multiplexing (FDM). Each separate baseband video signal is assigned a unique radio-frequency (RF) and up-converted to its assigned RF frequency so that multiple signals may simultaneously share the HFC network in accordance with FDM.
Programming signals from the hub or headend are typically transmitted as either analog signals or as digital transport streams. For example, each analog audio/video programming signal may occupy a 6 MHz channel. An example of a digital protocol by which the digital transport streams may be communicated is Moving Pictures Experts Group (MPEG or MPEG-2) which is described in more detail in the attached Appendix A. MPEG-2 is a standardized protocol by which moving pictures and accompanying sound tracks may be communicated digitally. This standard defines data packets, each including a packet header and data field. For digital networks or video server programs, multiple digital signals or programs may share a 6 MHz channel. The digital signals are typically transmitted using quadrature amplitude modulation (QAM). QAM-64 and QAM-256 are typical QAM modulations schemes. Typically, a combination of analog and QAM signals may be transmitted to cable subscribers via the HFC network using FDM. A QAM-256 modulator has a throughput of approximately 38 Mbps, which is equivalent to ten simultaneous audio/video programs, each at 3.8 Mbps VOD.
Multiple HFC networks or paths from each hub carry cable programming to different areas, such as different geographic neighborhoods. For non-VOD cable networks, an up-converter is typically used to broadcast programming signals over all of the HFC networks in a corresponding 6 MHz slot or RF channel frequency. Additional up-converters may broadcast additional signals to all of the HFC networks in other RF channels. Thus, each neighborhood receives all of the same programs over the corresponding RF channel frequencies.
For VOD, however, such a scheme of broadcasting VOD programming to every area or neighborhood may be inefficient. For example, assume that a hub feeds three HFC networks, where each HFC network provides data to a different neighborhood. Assume also, for example, that to meet demand for VOD, each neighborhood requires a maximum of twenty simultaneous programs. Assuming that one QAM channel is required for every ten programs, twenty programs is equivalent to 2 QAM channels or 12 MHz. For all three neighborhoods, the video server in the hub would need to support 60 simultaneous video programs so that 6 QAM channels would be required. If all 6 QAM channels are up-converted and broadcast on all three HFC networks, 36 MHz of bandwidth would be required on each HFC network. However, because each neighborhood may be expected to require only 12 MHz of bandwidth, this technique has a disadvantage of resulting in unnecessary bandwidth being provided to each neighborhood.
Therefore, what is needed is a technique and system for delivery of VOD data which does not suffer from the aforementioned drawback of typical systems. It is to this end that the present invention is directed.